Using mask in Wipe

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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bobequus
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Using mask in Wipe

Post by bobequus »

I have been trying to use the mask function in the wipe module, but it does not seem to work correctly. I wipe the image and when done, I have a small area that a bright star is overpowering that I want to tone down. I can make the mask (with lasso) I want and I get the "partial mask" note when I try to use it. But when I hit "DO", the entire image is affected. Same happens when I invert the mask as well. I also note that there is no slider for mask fuzz, which would be helpful. Any thoughts?
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Re: Using mask in Wipe

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Hi Bob,

I'm having some trouble understanding what it is you are looking to accomplish with Wipe. Could you describe the use case for Wipe for the problem you are having?

Masks in Wipe are used to tell it which pixels may be sampled, for the purpose of gradient and background bias modelling. Given you are mentioning a specific troublesome star, I'm not sure Wipe is the right tool for the job here?
Ivo Jager
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bobequus
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Re: Using mask in Wipe

Post by bobequus »

Thanks Ivo.
What you are saying is that the mask function when used in wipe, is only to choose an area (or set of pixels) for the wipe module to analyze, but that the result is applied to the entire image. That's good to know, but that is not masking. It's more like sampling or using selection in PS. When I use a mask, I am expecting to apply changes only to the area that has been selected. What I want to do is add a mask to a 'hot' area of the image (where the edge of a star is just in frame) and apply changes to reduce the brightness/exposure in that part of the image. In PS, I might use the 'burn' tool or play with the histogram for the area that was masked. With ST, the only way I see to tone down a bright area is with Wipe. I tried Color and HDR but none of the other modules seem to have the capability to do this.
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Re: Using mask in Wipe

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bobequus wrote:Thanks Ivo.
When I use a mask, I am expecting to apply changes only to the area that has been selected.
That is really quite a narrow definition of masking. Masking is - fortunately - used for many more things than just that this narrow use case. For example, just like someone would hide features of their face with a mask from the person looking at them, in Wipe a mask hides features of the image from the algorithms looking at it. It's really a classic example of a mask.
What I want to do is add a mask to a 'hot' area of the image (where the edge of a star is just in frame) and apply changes to reduce the brightness/exposure in that part of the image. In PS, I might use the 'burn' tool or play with the histogram for the area that was masked. With ST, the only way I see to tone down a bright area is with Wipe. I tried Color and HDR but none of the other modules seem to have the capability to do this.
Selective processing like this falls a little outside the realm of documentary photography and the purpose of StarTools. There are, of course, many tools that can be (ab)used for this purpose (even within StarTools - you could make a blend of two images with the Layer module for instance). Indeed though, if local re-touching is required, an application like The GIMP of Photoshop is more appropriate. However, as an astrophotographer I (and many others) would ideally want to know that your photo has been retouched in this way if it were presented as a photograph documenting reality, rather than an abstraction or art (for example like Apple did with M31). Hope that makes sense!
Ivo Jager
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Re: Using mask in Wipe

Post by bobequus »

I will try layering. That may do the trick. I'm not too concerned about this shot though as it was a quickie done for testing purposes and overexposed while I was waiting for my night's subject to rise. I only wanted to get a sense of focal length and composition so I have a better start at it when I decide to spend some real time on it.
However, as an astrophotographer I (and many others) would ideally want to know that your photo has been retouched in this way if it were presented as a photograph documenting reality, rather than an abstraction or art
I find this statement to be odd. For instance, I can go into the Color module, mask all the yellow stars, and manipulate the color to turn them red. Is that not retouching? Who would know? I don't feel that localized manipulation of a histogram or corrective exposure is "retouching". As someone who has spent years in a darkroom, dodging and burning of a silver print to enhance facial features or make a background more obscure was never considered "retouching". Perhaps to some, it is.
I'm new to ST and each time I use it, I get more comfortable and liking it more. Having the ability to locally work on exposure would be an asset for ST. I don't know how you would do this; new module or by modifying an existing one. But it is another way to keep the workflow moving along in ST without the need to interrupt and go into GIMP or PS and lose the Tracking feature. Thanks for your help.
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Re: Using mask in Wipe

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bobequus wrote:I can go into the Color module, mask all the yellow stars, and manipulate the color to turn them red. Is that not retouching?
Indeed, this would be a form of retouching.
Who would know?
That's precisely the problem - a layman would not know (as happened with the Apple image). However, your peers would likely raise it with you. That said, if it were uniformly applied to all stars (not, for example, just a few), then this consistency would give you some leeway as it can be argued all stars can be selected algorithmically. From an ethics point of view, you will notice, for example, that narrowband imagers who replaced their stars with RGB stars tend to mention this replacement.
I don't feel that localized manipulation of a histogram or corrective exposure is "retouching". As someone who has spent years in a darkroom, dodging and burning of a silver print to enhance facial features or make a background more obscure was never considered "retouching". Perhaps to some, it is.
Michael Covington, explains my personal stance quite well in his book "Astrophotography for the Amateur";

"It's important to make a distinction between processing an image and retouching. By "processing" I mean applying some algorithm uniformly to the whole picture to enhance the visibility of features that were already there. "Retouching" means altering particular pixels by deliberate action (...)"

I don't wish to prescribe to anyone how they should conduct astrophotography however. There are many shades of gray in between processing and retouching. I just hope the above serves as some context around why dedicated selective retouching tools like dodge & burn are not a focus of StarTools.
Ivo Jager
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